An ion milling method is known as one of methods for preparing a section of a sample for a purpose of analyzing by a scanning electron microscope.
An ion milling apparatus which performs the ion milling method is configured to include a sample chamber, an ion gun, a sample stage, a vacuum evacuation mechanism, and the like.
Examples of the ion gun which can be applied to the ion milling apparatus include, for example, a Penning-discharge-type ion gun. In PTL 1, an ion gun is disclosed for a purpose of decreasing an amount of sputtered particles which are deposited on an anode. The ion gun includes a first chamber, and an ion generation unit which generates ions by ionization of a gas in the first chamber. The ion generation unit includes an anode which is provided in the first chamber, a first cathode which is provided so as to face the first chamber and emits electrons, a gas supply unit which supplies a gas to the first chamber, and a magnetic field generation unit which generates a magnetic field in the first chamber. The electrons emitted by the first cathode are turned by the magnetic field generated by the magnetic field generation unit, and the turned electrons come into collision with the gas supplied by the gas supply unit, thereby generating the ions in the first chamber. An ion source with irregularities is provided in a first region of the front surface of the first cathode that faces the first chamber.